Steven, your number 4 doesn’t work for me, it just opens a new tab – seems to be a customized gesture and I’m interested in the section it’s in (Tools – Preferences – Advanced – Shortcut – Mousegestures+Edit – Quickfind: “duplicate”, what’s the headline?)

There are even more sophisticated buttons for duplicated tabs, e.g. have both tabs (the original and the duplicated tab) visible on the screen next to each other with “Split page” (only vertically worked for me) on Non-Troppo’s OperaWiki. The mentioned “Split-Screen Mode button” doesn’t work relyably (probably due to a timing problem), but you can do this manually:
Minimize all (via right click on tab + arrange OR menu window OR my minimize all button)
& Restore page (simply click on the tab)
& Duplicate page (described above)
& Tile horizontally or vertically (same place as minimize all)
If you have only one tab open it’s much easier, just duplicate and tile.
Background: only not minimized tabs are tiled, which is the same behaviour as on the Windows (XP) task bar.

For the “Create linked” button on Tomu’s TTT-page: this creates a linked tab from the current tab and if you click on any link on the current tab the link-target is opened in the linked tab (which you can drag off the Opera window to the desktop and further to a second screen). You can achieve the same manually by the Create linked menu entries next to the Duplicate tab entries (Right click on tab or Menu: Windows).